Evidence for a dusty warm absorber in NGC 3227 ?

Abstract

We have analyzed survey and pointed \ros PSPC observations of the Seyfert galaxy NGC 3227. Large amplitude X-ray variability is detected, with a factor $\sim$ 15 change in count rate within about 3 years. Smaller changes are seen on the timescale of days, the largest being a factor of 3.5. No strong spectral variability is found throughout the pointed observation. The X-ray spectrum is modeled in terms of warm absorption and both, a dust-free warm absorber and one with internal dust, give an excellent spectral fit. Additionally using multi-wavelength observations of NGC 3227, the dusty warm absorber is favored and suggested as an explanation for the lack of a large cold absorbing column in the soft X-ray region despite excess reddening along the line of sight. Self-consistent re-calculation of the models including Galactic-ISM-like dust results in an ionization parameter log U = -0.25 and a column density log N_w = 21.8 of the warm absorber. X-ray variability and dust survival arguments are used to constrain the density and further properties of the ionized material. The influence of dust and other parameters on the thermal stability of the warm absorber is investigated. Predictions are given for the absorber-intrinsic optical--UV line emission and absorption.